For example, a mobile communication terminal such as a cellular telephone communicates by selecting a cell to be a local station out of cells formed by a plurality of base stations and sending and receiving radio signals.
Here, a mobile communication terminal corresponding to the W-CDMA (Wideband-Code Division Multiple Access) system measures qualities of radio signals in a local station and peripheral cells periodically, for example, during waiting. In this case, setting concerning the quality measurement such as designation of peripheral cells to be objects for measuring qualities of radio signals is regulated based on system information notified from the local station.
Such a mobile communication terminal can compare a result of the quality measurement with criteria for reselection of a cell defined in advance, autonomously perform the reselection of a cell to shift a resident zone (zone shift) and switch the local station. Here, a group of parameters for regulating the criteria for reselection of a cell is notified to the mobile communication terminal by system information from the local station.
Here, a mobile communication network may apply an algorism called a hierarchical cell structure (HCS) to regulate the criteria when the mobile communication terminal performs the zone shift. A set value in applying this algorism is notified to the mobile communication terminal by the system information from the local station.
This HCS allocates values indicating an HCS priority to the local station and the peripheral cells using the system information from the local system, and the mobile communication terminal uses this HCS priority in processing for reselecting a cell in switching the local station to perform the zone shift. The HCS priority is for setting criteria for selection for the mobile communication terminal to switch the peripheral cells to the local station for each peripheral cell in performing the zone shift.
That is, for example, the HCS allocates an HCS priority higher than the present local station to peripheral cells for which the mobile communication network side determines preferential selection is desirable in the zone shift by the mobile communication terminal. On the other hand, the HCS allocates an HCS priority lower than the present local station to peripheral cells for which the mobile communication network side determines subordinate selection is desirable.
In addition, in applying this HCS, processing for determining whether or not the mobile communication terminal is moving at a high speed may be executed. A group of parameters used in this determination processing is also notified to the mobile communication terminal by the system information from the local station.
This determination processing determines whether or not the number of times the mobile communication terminal reselects cells and performs the zone shift during the period until a predetermined measurement termination time T_CR_MAX elapses has exceeded a predetermined threshold value N_CR and, if it is determined that the threshold value has been exceeded, considers the mobile communication terminal is in a rapid moving state to change the criteria for reselection of a cell.
For example, in ordinary criteria for reselection of a cell (in a non-rapid moving state), cells with a higher HCS priority is selected preferentially. On the other hand, in criteria for reselection of a cell in a rapid moving state, cells with a lower HCS priority is selected preferentially.
In this case, this means that the mobile communication network regulates such that cells with a high HCS priority is selected preferentially when the mobile communication terminal is in the non-rapid moving state and cells with a low HCS priority is selected preferentially when the mobile communication terminal is in the rapid moving state.
For example, FIG. 8 is a flow chart for explaining an example of processing for detecting that a conventional moving communication terminal is moving at a high speed.
The mobile communication terminal initializes a variable V_CR, which indicates the number of times cells are reselected during the period until a predetermined measurement termination time T_CR_MAX elapses, as zero (step S20).
Next, the mobile communication terminal starts up a measurement section timer for measuring time to measure the number of times of reselection of a cell to make it possible to detect that the predetermined measurement termination time T_CR_MAX has elapsed (step S21).
The mobile communication terminal determines whether or not reselection of a cell has occurs (step S22) and, upon determining that reselection of a cell has occurred (YES in step S22), increments the variable V_CR by one (step S23). On the other hand, upon determining that reselection of a cell has not occurred (NO in step S22), the mobile communication terminal determines whether or not time measured by the timer has passed the measurement termination time T_CR_MAX (step S24).
Upon determining that the time measured by the timer has not passed the measurement termination time T_CR_MAX (NO in step S24), the mobile communication terminal returns the processing to step S22 and detects occurrence of reselection of a cell.
On the other hand, upon determining that the time measured by the timer has passed the measurement termination time T_CR_MAX (YES in step S24), the mobile communication terminal determines whether or not the number of times of reselection indicated by the variable V_CR has exceeded a predetermined threshold value N_CR (step S25).
Upon determining that the number of times of reselection indicated by the variable V_CR has not exceeded the threshold value N_CR (NO in step S25), the mobile communication terminal returns the processing to step S20 and continues the processing for detecting movement at a high speed.
On the other hand, upon determining that the number of times of reselection indicated by the variable V_CR has exceeded the threshold value N_CR (YES in step S25), the mobile communication terminal, considering that it has been detected that it is moving at a high speed, executes processing for shifting to a rapid moving state such as changing criteria for reselection of a cell (step S26).